Anatomical information available on the inner ear in lower vertebrates is limited. Studies which have been reported provide diverse information on various aspects of the membranous labyrinth, but each deals with one or a limited number of species which are usually not closely related. In this proposed project selected species of catfishes will be used to investigate phylogenetic changes in the morphology, histology and ultrastructure of the inner ear and to study in detail the cellular components and overlying otolithic membrane. All areas of the labyrinth will be investigated, but major emphasis will be placed upon the saccule. This project will utilize conventional methods of light microscopy and transmission and scanning electron microscopy. Data obtained should enhance the knowledge of the vertebrate inner ear, and this information when combined with physiological data will lead to a better understanding of the significance of auditory and vestibular structures and the relation of these structures to the function of the inner ear in all vertebrates.